Internally finned tube having enhanced nucleation centers, heat exchangers, and methods of manufacture

ABSTRACT

Tubing having internal fins projecting inward from the tube wall, each fin having an external surface that includes multiple acute interior angles or crevices that may form nucleation boiling sites, heat exchangers comprising such tubing, and methods of making same. Acute angles, crevices, or elongated slits may be formed in the sides, center, or both, of the fins or between the fins and the tube wall, and convex rounded surfaces may be provided therebetween. Fins may be parallel to the tube centerline or helically wound. Tubing may be expanded with a bullet which may form an interference fit with external fins, may modify the fins to create more effective nucleate boiling cavities, or both.

CLAIM OF PRIORITY

This patent application claims priority to, and incorporates by reference, U.S. provisional patent application 61/058,401 titled Internally Finned Tube Having Enhanced Nucleation Center, Heat Exchangers, and Air Conditioning Units, which was filed on Jun. 3, 2008.

FIELD OF THE INVENTION

This Invention relates to heat exchangers, including heat exchangers used in air conditioning units, and to methods and equipment for making heat exchangers.

BACKGROUND OF THE INVENTION

Heat exchangers have been used for some time to transfer heat from a warmer fluid to a cooler fluid, including in air conditioning units for cooling or heating (or both), spaces that people occupy, such as within buildings, vehicles, or the like. FIG. 1 illustrates an example of a heat exchanger 10 that may serve as an evaporator or a condenser in an air conditioning unit, for example, to transfer heat between a refrigerant and air, for instance.

Refrigerant, which may be liquid, gas, or a combination thereof, may pass through tubing 11, exchanging heat with air that may pass by external fins 12, for example. External fins 12 may be formed from flat sheets of metal, such as aluminum, which may have holes formed or stamped therethrough for passage of tubing 11. These holes may be formed in a manner forming collars 13 (e.g., shown in the expanded view in the lower right corner), in some embodiments, which may be thicker than the sheet metal of external fins 12, providing strength to external fins 12 in this location as well as, in some embodiments, spacing external fins 12 apart from each other and providing additional surface area for heat transfer between external fins 12 and tubing 11.

In some prior art embodiments, an interference fit has been used between tubing 11 and external fins 12. Such an interference fit has enhanced heat transfer between tubing 11 and external fins 12, and has also provided a structural connection between tubing 11 and external fins 12, in some embodiments. In some cases, such an interference fit has been created by passing a round tool called a bullet through tubing 11 to expand tubing 11 after tubing 11 has been passed through the holes and collars 13 in external fins 12, for example.

In certain instances, tubing 11 was formed into long U-shaped tubes or “hairpins” 14 that were inserted through two sets of holes and collars 13 in external fins 12, and then a bullet was passed through each of the two sides of the hairpin 14 to expand tubing 11 and create the interference fit. Then short U-shaped tubes or 180 degree bends or fittings 15 were brazed or otherwise attached between the hairpins 14 to produce one or more continuous pathways of tubing 11 through heat exchanger 10. In some embodiments, some hairpins 14 (e.g., at the top, bottom, or both of heat exchanger 10, were brazed or otherwise attached to one or more headers 16.

In the embodiment shown, external fins 12 are enhanced with louvers 17 to increase heat transfer between the air and external fins 12. Also in the embodiment illustrated, end plates 18 and 19 have been used to provide additional strength, stiffness, or both, to heat exchanger 10.

Resistance to the transfer of heat between tubing (e.g., 11) and the refrigerant or other fluid therein can reduce the effectiveness of a heat exchanger (e.g., 10). In addition, it is known that small gaps, cavities, or crevices can act as nucleation sites or centers to promote boiling at a faster rate than boiling would otherwise occur. It is known in the art that sharp grooves, for example, create effective nucleate boiling sites. It is also known that partially closed cavities and crevices are even more effective than grooves, but, in the past, have been difficult to achieve in practice.

U.S. Pat. No. 4,040,479 (by Bonnie Campbell and Klaus Rieger) describes finned tubing with narrow gaps in external fins to create nucleate boiling sites. Furthermore, tubing (e.g., 11) that has been used in residential air conditioner coils (e.g., similar to heat exchanger 10) has been made with low profile internal grooves which are either parallel with the tube axis or spiraled on the inside tube wall. These grooves typically produce some increased heat-transfer performance in evaporators but little or no performance increase in condensers. However, groves, notches, and the like, on the inside of the tube wall create stress concentration factors and reduce the pressure capacity of the tubing or may induce stress failures.

Needs, potential for benefit, and room for improvement exist for transferring heat more effectively between tubing (e.g., 11) and fluids such as refrigerant contained or flowing therein. In addition, in applications where nucleate boiling is part of the process, needs, potential for benefit, and room for improvement exist for tubing and methods of making tubing wherein nucleate boiling centers are provided within the tubing in greater numbers, without decreasing (at least to the same degree) the structural integrity of the tubing, without creating (at least to the same degree) stress concentration factors in the tubing wall, or a combination thereof, as examples. Room for improvement exists over the prior art in these and other areas that may be apparent to a person of ordinary skill in the art having studied this document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a prior art heat exchanger showing, among other things, tubing and external fins, but lacking certain features of various embodiments of the invention, such as internal fins;

FIG. 2 is a perspective view of an embodiment of a heat exchanger, or a section of a heat exchanger, having an embodiment of internally finned tubing having multiple acute interior angles on the fins that may form nucleate boiling cavities, for example;

FIG. 3 is a perspective view of an embodiment of a piece of internally finned tubing prior to expansion, wherein the fins and interior angles are parallel to the centerline of the tubing;

FIG. 4 is a perspective view of the internally finned tubing of FIG. 3 after expansion, which may form nucleate boiling cavities, for example;

FIG. 5 is a perspective view of another embodiment of a piece of internally finned tubing prior to expansion, wherein the fins and interior angles are helically wound around the centerline of the tubing;

FIG. 6 is a perspective view of the internally finned tubing of FIG. 5 after expansion, which may form nucleate boiling cavities, for example;

FIG. 7 is a perspective view of a different embodiment of a piece of internally finned tubing prior to expansion, wherein the fins and interior angles are parallel to the centerline of the tubing;

FIG. 8 is a perspective view of the internally finned tubing of FIG. 7 after expansion, which may form nucleate boiling cavities, for example;

FIG. 9 is a perspective view of yet another embodiment of a piece of internally finned tubing prior to expansion, wherein the fins and interior angles are parallel to the centerline of the tubing;

FIG. 10 is a perspective view of the internally finned tubing of FIG. 9 after expansion, which may form nucleate boiling cavities, for example;

FIG. 11 is a perspective view of still another embodiment of a piece of internally finned tubing prior to expansion, wherein the fins and interior angles are parallel to the centerline of the tubing;

FIG. 12 is a perspective view of the internally finned tubing of FIG. 11 after expansion, which may form nucleate boiling cavities, for example;

FIG. 13 is an isometric view of an example of a bullet that can be used to expand certain embodiments of the tubing;

FIG. 14 is a perspective view of an embodiment of a heat exchanger, or a section of a heat exchanger, having the embodiment of internally finned tubing shown in FIGS. 7 and 8 and showing an example of a bullet being used to expand the tubing and modify the internal fins, which may create more effective nucleate boiling cavities, for instance;

FIG. 15 is a close up isometric view of an example of a bullet being used to expand the internally finned tubing shown in FIGS. 7 and 8 and modify the internal fins, for example, to create more effective nucleate boiling cavities;

FIG. 16 is an isometric view of another example of a bullet that can be used to expand certain embodiments of the tubing and modify the internal fins, for instance, to create more effective nucleate boiling cavities;

FIG. 17 is a perspective view of an embodiment of a heat exchanger, or a section of a heat exchanger, having the embodiment of internally finned tubing shown in FIGS. 11 and 12 and showing the bullet of FIG. 16 being used to expand the tubing and modify the internal fins, for instance, to create more effective nucleate boiling cavities; and

FIG. 18 is a flow chart illustrating various methods of making a heat exchanger, for instance, that has enhanced heat transfer characteristics.

SUMMARY OF PARTICULAR EMBODIMENTS OF THE INVENTION

This invention provides, among other things, enhanced tubing for conducting heat between a first fluid within the tubing and a second fluid exterior to the tubing, various air conditioning units that may have an evaporator, condenser, or both, manufactured in accordance with an embodiment of the invention, various HVAC systems and buildings having such systems, certain tools or bullets for expanding internally finned tubing in accordance with an embodiment of the invention, various heat exchangers for effectively transferring heat energy between a first fluid and a second fluid, for example, and various enhanced evaporators for use in an air conditioning unit, for instance, for residential use, as well as certain air conditioning units and HVAC systems having such heat exchangers or evaporators, as further examples.

Various embodiments provide, for example, as an object or benefit, that they partially or fully address or satisfy one or more of the needs, potential areas for benefit, or opportunities for improvement described herein, or known in the art, as examples. Certain embodiments provide for transferring heat more effectively between tubing (e.g., 11) and fluids such as refrigerant contained or flowing therein. In addition, in applications where nucleate boiling is part of the process, certain embodiments provide, for example, as an object or benefit, that they provide tubing, heat exchangers, evaporators, condensers, air conditioning units, HVAC systems, or buildings having such systems, or methods of making such things wherein nucleate boiling centers are provided within the tubing in greater numbers, without decreasing (at least to the same degree) the structural integrity of the tubing, without creating (at least to the same degree) stress concentration factors in the tubing wall, or a combination thereof, as examples.

In specific embodiments, the invention provides enhanced tubing, for example, for conducting heat between a first fluid within the tubing and a second fluid exterior to the tubing. In a number of embodiments, the tubing includes at least one tube wall defining an interior passageway, and multiple internal fins projecting inward from the at least one tube wall, each internal fin having an external surface that includes multiple acute interior angles.

In some embodiments, the internal fins have sides, and in particular embodiments, at least multiple of the acute interior angles are formed in the sides of the internal fins. Further, in certain embodiments at least a portion of the acute interior angles are formed between the internal fins and the tube wall. Moreover, in specific embodiments, each internal fin has a first side and a second side, and for each of the internal fins, a first acute interior angle is formed between the first side of the internal fin and the tube wall, and a second acute interior angle is formed between the second side of the internal fin and the tube wall, for example.

Additionally, in a number of embodiments, each internal fin has a center, and each of the internal fins includes one of the acute interior angles at the center of the internal fin. Furthermore, in some embodiments, the tubing has a centerline and the multiple internal fins are parallel to the centerline, the acute interior angles are parallel to the centerline, or both. On the other hand, in some embodiments, the multiple internal fins are helically wound around the centerline, the acute interior angles are helically wound around the centerline, or both.

In a number of embodiments, each internal fin includes an elongated slit therein. In some embodiments, each internal fin has a center, and the elongated slit is in the center of the internal fin, for example. In addition (or in the alternative), in some embodiments, the multiple internal fins include at least four internal fins, the acute interior angles are between 20 and 85 degrees, or both, for instance. Furthermore, in various embodiments, each of the multiple internal fins includes at least one convex rounded surface between at least two of the acute interior angles. In some embodiments, in fact, each of the multiple internal fins includes multiple convex rounded surfaces between the acute interior angles.

Further, in some embodiments, the tubing includes a first straight section of tubing, a second straight section of tubing, and a 180 degree bend between the first section and the second section, for example. Moreover, in a number of embodiments, the tube wall has an exterior surface that includes scalloped relief areas. In particular embodiments, for instance, there is one of the scalloped relief areas across the tube wall from each one of the internal fins.

In other specific embodiments, the invention provides a method of making a heat exchanger that has enhanced heat transfer characteristics, for example. In various embodiments, such a method may include, for instance, in any order at least certain acts. Such acts may include, for example, forming tubing having at least one tube wall defining an interior passageway, and multiple internal fins projecting inward from the at least one tube wall. Another example of an act is stacking multiple exterior fins, each exterior fin have multiple holes therethrough. In a number of embodiments, the act of stacking includes lining up the holes in the multiple exterior fins, for instance. Other acts, in various embodiments, include passing the tubing through the holes in the multiple exterior fins, expanding the tubing to create an interference fit between the tubing and the holes, modifying the internal fins to create more effective nucleate boiling cavities, or a combination thereof, as examples.

In particular embodiments, the invention also specifically provides various embodiments of heat exchangers, for instance, for effectively transferring heat energy between a first fluid and a second fluid, for example. In various embodiments, the heat exchanger includes multiple sections of tubing, each section having at least one tube wall defining an interior passageway, and multiple internal fins projecting into the passageway from the (at least one) tube wall, each internal fin having multiple crevices forming nucleation boiling sites. In some embodiments, multiple external fins have holes, and the multiple sections of tubing pass through the holes and form an interference fit with the holes, for example. Further, some such heat exchangers include multiple 180 degree bends joining the multiple sections of tubing.

In addition, various other embodiments of the invention are also described herein, and other benefits of certain embodiments may be apparent to a person of ordinary skill in the art.

Detailed Description of Examples of Embodiments

FIGS. 2 to 18 illustrate examples of tubing structures and fabrication processes and devices for producing various embodiments of heat transfer tubes (e.g., which may be used similarly to tubing 11 described above) utilizing, in many embodiments, internal fins, multiple nucleation boiling sites, or both, as examples, for improved heat transfer performance. The application of a number of embodiments include extruded aluminum tubes used (e.g., similarly to tubing 11) in tube-fin heat exchanger coils (e.g., similar to heat exchanger 10) for residential air conditioners, for example. Other embodiments may be used for other purposes, made of another material, made in a different way, contain a different fluid, or a combination thereof, as further examples.

A number of embodiments may result in measurable increases in evaporator or condenser performance (or both). Stronger evaporator performance may be achieved, in some embodiments, by the creation of highly-effective nucleation centers, for instance. Various embodiments use a tube expansion process to create crevices, cavities, or both, from grooves to gain evaporating performance. Moreover, in a number of embodiments, internal fins may also (or instead) enhance non-boiling heat transfer which may also increase condenser performance, for example, due to the presence of extended surfaces, (i.e., fins), on the inside of the tube. Thus, various embodiments may be used to provide either evaporator or condenser improvements, or both, in a single tube design for superior performance in one or both applications.

Referring to the drawings (e.g., FIGS. 1-18), in many embodiments, achieving a desired configuration in the inside wall of the tubes requires starting with an appropriate internally finned tube profile and subsequently modifying the internal fins during an expansion process. FIG. 1 illustrates a prior art heat exchanger showing, among other things, tubing 11 and external fins 12, but lacking certain features of various embodiments of the invention, such as internal fins. FIG. 2 illustrates an embodiment of a heat exchanger, heat exchanger 20 (or a section of a heat exchanger), having an embodiment of internally finned tubing, tubing 25. In FIG. 2, the bottom two tubes 22 and 23 are shown expanded and the top tube 21 is shown prior to expansion. However, in practice all tubes (e.g., 21-32) may be expanded simultaneously. Scallops 26 can be seen on top tube 21. During the expansion process the scallops (e.g., 26) are pressed out, in the embodiment illustrated, which is why no scallops (e.g., 26) are show on the exterior of tubes 22 and 23.

FIGS. 3, 5, 7, 9 and 11 illustrate various embodiments of tubes (25, 55, 75, 95, and 115) prior to expansion, and FIGS. 4, 6, 8, 10 and 12 illustrate various tubes (25, 55, 75, 95, and 115) that have been expanded. FIG. 3 shows a piece of internally finned tubing 25 prior to expansion, wherein the fins 31 and interior angles are parallel to the centerline of the tubing. FIG. 4 is a perspective view of the internally finned tubing 25 of FIG. 3 after expansion, having nucleate boiling cavities 41, 42, 43, and 44, for example. FIGS. 5 and 6 show tube embodiment 55 with fins 51 and acute angles 61, 62, 63, and 64 helically wound around the centerline of the tube 55.

FIGS. 13 and 16, show examples of expansion bullets 130 and 160 with and without forming fingers 131.

FIG. 14 illustrates an embodiment of a heat exchanger, heat exchanger 140 (or a section of a heat exchanger), having the embodiment of internally finned tubing 75 shown in FIGS. 7 and 8 and showing an example of a bullet (e.g., bullet 130) being used to expand the tubing 75 (shown in FIGS. 7 and 8) and modify the internal fins 71, to create more effective nucleate boiling cavities 81, 82, and 83, for instance. FIG. 14 illustrates a method of expanding the tubes (tube 75 shown), wherein the bottom tube 143 has the expansion bullet 130 part way down the tube (143), the center tube 142 shows the expansion bullet 130 just starting into the tube (142) and the top tube 141 is shown with the expansion bullet 130 not yet engaged in the tube (141). In practice, all tubes (e.g., 141, 142, and 143) may be expanded simultaneously or in a different order than illustrated. FIG. 15 is a close up view of the center tube 142 of FIG. 14 where the expansion bullet 130 is just starting into the tube 142. FIG. 17 is similar to FIG. 14 except tubes 115 with heart-shaped fins 111 and smooth bullets 160.

A starting tube configuration, (e.g., for tubes 25, 55, 75, 95, or 115) in a number of embodiments, is an aluminum extrusion with specially shaped integral fins (e.g., 31, 51, 71, 91, or 111) inside the tube. In various embodiments, the internal fins contain V-shaped grooves (e.g., as shown in FIGS. 3, 5, and 7) in their sides, for example, and, in some embodiments (e.g., depending on tube diameter), an elongated slit cavity (e.g., as shown in FIGS. 3 and 5), for instance, in the center. During the expansion process (e.g., as shown in FIGS. 14, 15, and 17), in particular embodiments, these internal fins (e.g., 31, 51, 71, 91, or 111) are reconfigured to a desired final shape. In some embodiments, the expander bullet (e.g., 130) is uniquely shaped, which may be to accommodate the internal finned profile of the tube (e.g., 31, 51, 71, 91, or 111) and, in some embodiments, the bullet (e.g., 130) may self-align during insertion.

In various embodiments, enhanced evaporating heat transfer may be achieved, among other things, by creating multiple nucleation boiling sites (e.g., 41, 42, 43, 44, 61, 62, 63, 64, 81, 82, 83, 101, 102, 121, 122, 123, or a combination thereof). In some embodiments, for example, this may be accomplished in two steps: 1) the tube may be initially formed (e.g., extruded) with sharp V-shaped grooves, for instance, in the sides of the fins (e.g., 60 degree grooves) (e.g., as shown in the sides of the fins in FIGS. 3, 5, and 7), and, in different embodiments, with or without an elongated slit cavity (e.g., as shown in FIGS. 3 and 5) in the center of each fin (e.g., fin 31 or 51), for instance. In other embodiments, FIGS. 9 to 12 show embodiments where crevices (e.g., 101, 102, 121, and 122) are formed between the fins (e.g., 91 and 111) and the tubing wall (e.g., 37, 57, 77, 97, or 117), as other examples. In certain embodiments or applications, the presence of these fins alone improves heat transfer performance, even before expansion of the tubing. The second step is accomplished, in a number of embodiments, during the tube expansion process, wherein the (e.g., internal) fins are reconfigured to a more effective profile, for example (e.g., as shown in FIGS. 14 and 17).

In particular embodiments, during expansion, the (e.g., internal) fins are compressed, reforming the grooves near the fin tips into crevices, and, in some embodiments, the slits in the fin tips may be partially closed creating more effective nucleate boiling cavities, for example (e.g., as shown in FIGS. 4 and 6). Further, as shown in FIGS. 9-12, in some embodiments, grooves, angles, or crevices are formed between the sides of the fins and the tubing wall. In a number of embodiments, one or more of these changes over prior configurations further improves nucleate boiling performance. In addition, in many embodiments, the final fin profiles also improve non-boiling heat transfer.

In some embodiments, tubing may be expanded differently, depending on whether it is going to be used in an application (e.g., an evaporator) where boiling will take place, or an application (e.g., a condenser) where boiling will not take place. For example, in applications where boiling will take place, a different bullet may be used, which may compress the internal fins more, creating better nucleate boiling sites. On the other hand, in applications where boiling is not part of the heat transfer process, the internal fins may not be compressed, may be compressed to a lesser extent, or may be compressed differently to form a different fin shape (e.g., to increase surface area or penetration into the interior of the tubing), as examples.

In certain embodiments, the height of the (e.g., internal) fins are selected such that the fins are compressed during expansion, in particular embodiments, causing the grooves (e.g., near the tip of the fins as shown in FIGS. 3-6, or between the fins and tubing wall, as shown in FIGS. 9-12) to be reconfigured, for example, as described above. In particular embodiments, the initial height of the fins is selected to be greater than the groove depth in the expander bullet, for example, by an amount needed to achieve the desired fin height compression. Further, in a number of embodiments, the expander bullet is appropriately tapered, beveled, or both, and, in some embodiments, is configured to rotate and self align with the (e.g., internal) fins during insertion.

Further, in various embodiments, the (e.g., internal) fin thickness may be selected to be sufficient to transfer (e.g., conduct) heat between the tube wall and fin tip. In particular embodiments, the fin thickness may be selected to meet this objective while using a minimum amount of material, for example. Thus, in some embodiments, fin efficiency may be considered. In some embodiments, the selection of fin thickness may take into consideration a need for the fin to be able to withstand the expansion process and deform into the desired end shape, as another example.

In some embodiments, the total number of (e.g., internal) fins may be selected, for instance, by making an appropriate balance between surface area enhancements, reduced heat transfer coefficient (e.g., lower Reynolds Number) and material cost considerations. In various embodiments, the permissible height of the fins after expansion may be limited by the diameter of the bullet expander rod, as another consideration. Further, in particular embodiments, side clearances between the expander bullet and fins may permit the release of any trapped air, lubricant, or both, when expanding blind tubes, for example, in hairpin configurations. Even further, in some embodiments, shallow scallops, for example, may be provided on the outside diameter of the tube opposite the (e.g., internal) fins, for instance, to provide relief from overexpansion in these areas due to bullet forces on the fin tips.

A number of embodiments (e.g., as shown in FIGS. 3-8) confine grooves, notches, and cavities, for example, to the non-stressed fin areas instead of the tube wall which must contain and withstand the stress of high pressures. This avoids stress concentration and risk of consequent failure, in various embodiments. In certain embodiments, the expanded tube profile contains the desired crevices and cavities for enhancing nucleate boiling performance without weakening the tubes. In particular embodiments, this is accomplished while delivering superior non-boiling heat transfer performance, as well, for example, due to the extended (e.g., internal) fin surfaces. In some embodiments, the crevices formed from grooves are tapered and are therefore capable of accommodating fluids having different physical properties, such as different surface tension, different latent heat of vaporization, or both. Further, in some embodiments, some crevices may be formed by tearing (e.g., as shown in FIG. 12).

Specially shaped, expander bullets (e.g., 130) may be used, in many embodiments, to modify the internal fin profiles to form effective nucleate boiling crevices. In some embodiments, this bullet contains special features to guide and align the bullet grooves with the spaces between (e.g., internal) fins in the tube, upon entry. In certain embodiments, the bullet may be self aligning, for example. FIG. 16 illustrates another embodiment of a bullet, bullet 160, which is simpler in configuration.

Tubing described herein may be used in heat exchangers, such as those described herein, which may be used, among other things, as evaporators, condensers, or both, for instance, in residential, commercial, or automotive air conditioning systems, in refrigerators or freezers, in vehicle radiators, in chilled or heated water air handlers, in oil coolers, in boilers, in power plants, in (e.g., flat plate or parabolic trough) solar collectors, or the like. A number of embodiments offer particular improvement in heat transfer in applications where boiling takes place, for example. Embodiments of the invention include tubing, heat exchangers, evaporators, condensers, air conditioning units, air handlers, heat pumps, HVAC systems, buildings having HVAC systems, equipment such as bullets for making such equipment, and method of making, improving such items. Further embodiments include methods of enhancing tubing for heat transfer, methods of promoting nucleate boiling, methods of enhancing heat transfer, for example, in tubing or heat exchangers, methods of providing nucleate boiling centers, for instance, in tubing or heat exchangers, and the like. FIG. 18 illustrates an example of a method.

Various embodiments of the invention include various combinations of the features described herein or shown in the drawings (e.g., FIGS. 1-18). Certain embodiments of the invention also contemplate various procedures or methods of providing or obtaining different combinations of the components or structure described herein. Such procedures may include acts such as providing various components described herein, and providing components that perform functions described herein, as well as packaging, advertising, and selling products described herein, for instance. Particular embodiments of the invention also contemplate various means for accomplishing the various functions described herein or apparent from the structure described.

For example, in specific embodiments, the present invention provides enhanced tubing (e.g., as shown in FIGS. 3-12) for conducting heat between a first fluid within the tubing and a second fluid exterior to the tubing. In some such embodiments, the tubing (e.g., 25, 55, 75, 95, or 115) may have at least one tube wall (e.g., 37, 57, 77, 97, or 117) defining an interior passageway (e.g., 38), and multiple internal fins (e.g., 31, 51, 71, 91, or 111) projecting inward or into the passageway (e.g., 38), for example, from the tube wall. In certain embodiments, each internal fin may have an external surface (e.g., 39) that may have at least one or multiple V-shaped grooves or acute interior angles (e.g., 54 as shown in FIG. 5), as examples. In some embodiments, at least some of the acute interior angles may be formed in the sides of the internal fins, for example, as shown in FIGS. 3, 5, and 7.

In some embodiments, at least a portion of the acute interior angles are formed between the internal fins and the tube wall (e.g., 94, 96, and 114 shown in FIGS. 9 and 11). In certain embodiments, each internal fin (e.g., 71 or 91) has a first side (e.g., 78 and 98 shown in FIGS. 7 and 9) and a second side (e.g., 79 or 99), and for each of the internal fins (e.g., 91), a first acute interior angle (e.g., 96) is formed between the first side (e.g., 98) of the internal fin (e.g., 98) and the tube wall (e.g., 97), and a second acute interior angle (e.g., 94) is formed between the second side (e.g., 99) of the internal fin (e.g., 91) and the tube wall (e.g., 97). An alternate embodiment is shown in FIG. 11. Further, in some embodiments, each of the internal fins has a crevice or one of the acute interior angles at the center of the internal fin (e.g., as shown in FIGS. 3-6). In particular embodiments, multiple crevices that are shaped to promote nucleate boiling are defined on a first side by the tube wall and on a second side by the internal fins projecting into the passageway (e.g., crevices 101, 102, 121, and 122 as shown in FIGS. 10 and 12).

In a number of embodiments, the multiple internal fins, the acute interior angles, or both may be parallel to the centerline of the tubing (e.g., as shown in FIGS. 2-4 and 7-12) or may be helically wound around the centerline (e.g., as shown in FIGS. 5-6), as examples. In particular embodiments, each internal fin further includes an elongated slit therein (e.g., 36 as shown in FIGS. 3-6). In fact, in some embodiments, the elongated slit (e.g., 36) may be in the center of the internal fin (e.g., as shown in FIGS. 3-6). In different embodiments, the multiple internal fins may include at least four internal fins, at least six internal fins, at least eight internal fins, at least ten internal fins, at least 12 internal fins, at least 16 internal fins, or may have precisely 10, 12, or 16 internal fins, as examples. In certain embodiments, the multiple internal fins may all be substantially identical. Further, in various embodiments, each of the multiple internal fins has two (e.g., as shown in FIG. 10), three (e.g., as shown in FIG. 12), at least four (e.g., as shown in FIGS. 3-8), at least six (e.g., as shown in FIGS. 3-8), or precisely six (e.g., as shown in FIGS. 3 and 5) or precisely seven (e.g., as shown in FIG. 7) of the acute interior angles, as examples.

In a number of embodiments, one or more of the acute interior angles may be between 20 and 85 degrees, between 30 and 80 degrees, between 45 and 75 degrees, between 50 and 70 degrees, between 55 and 65 degrees, or even between 58 and 62 degrees, as examples. In certain embodiments, each of the multiple internal fins, for example, includes one or more convex rounded surfaces between the acute interior angles (e.g., as shown in FIGS. 3-12). In some embodiments, some or all of these convex rounded surfaces may feature a section of a circle, for example. In some embodiments, the tubing may have a first straight section, a second straight section, and a 180 degree bend (e.g., 15 shown in FIG. 1) between the first section and the second section (e.g., a hairpin 14). Further, in various embodiments, the exterior surface of the tube wall may have scalloped relief areas (e.g., as shown in FIGS. 2, 3, and 5), and, in some embodiments, there may be one of the scalloped relief areas across the tube wall (e.g., on the opposite side of the tube wall) from each one of the internal fins, for example.

The invention also provides, in different embodiments, various methods of making heat exchangers that have enhanced heat transfer characteristics. Method 180 shown in FIG. 18 is an example of such a method. Certain methods may include (e.g., in any order, except where a particular order is specified or would be necessary or apparent) at least certain acts. Method 180 includes acts of forming tubing (act 181), stacking multiple exterior fins (act 182) (e.g., wherein each exterior fin may have multiple holes therethrough and the act of stacking (e.g., 182) may include lining up the holes in the external fins), and passing the tubing through the holes (act 183), in the external fins. Method 180 also includes, in the embodiment illustrated, expanding the tubing (act 184), for instance, to create an interference fit between the tubing and the holes, and modifying the internal fins (act 185) into crevices, for example, to create more-effective nucleate boiling cavities (e.g., by forming tighter angles, crevices, or cracks).

In some such embodiments, the tubing may have the structure of one or more of the embodiments described above, the modifying of the internal fins (e.g., act 185) may include reforming the acute interior angles mentioned above, or both, as examples. Further, in some embodiments, the acts of expanding the tubing (act 184) and modifying the tubing (act 185), or both, may be accomplished by passing a (e.g., single) bullet through the tubing, for instance. Thus, in some embodiments, acts 184 and 185 may be performed at the same time. In other embodiments, internal fins may be formed or modified by passing multiple bullets, through the tubing in multiple passes, as other examples. Further, in some embodiments, the act of forming the tubing (act 181) may include extrusion (e.g., extruding metal to form the internally finned tubing).

Moreover, the invention also provides, in particular embodiments, various air conditioning units that may have an evaporator, condenser, or both, manufactured in accordance with one or more of the above methods, and certain heat exchangers which may be manufactured in accordance with one or more of the above methods, as well as various HVAC systems and buildings that have a heat exchanger or air conditioning unit manufactured in accordance with one or more of the above methods.

Certain tools or bullets (e.g., 130 and 160) are contemplated for expanding internally finned tubing, for instance, to create an interference fit with multiple exterior fins, and also, in some embodiments, for compressing internal fins to form more-effective nucleate boiling sites, for example. In some such embodiments, the bullet (e.g., 130) may have an annular hub that may have a front end and a back end, and multiple teeth projecting radially outward from the annular hub. In some embodiments, the bullet has a major diameter measured at tops of the teeth, a minor diameter measured at bottoms of the teeth, or both. In various embodiments, the major diameter may be selected to expand a wall of the tubing to create the interference fit, the minor diameter may be selected to compress the internal fins to form more-effective nucleate boiling sites, or both, as examples. In particular embodiments, a bullet may have raised ribs between the teeth, which may be midway between the teeth, for example.

In some embodiments, the teeth may have a first included angle for alignment when inserting the bullet into the tubing, the teeth may have a second included angle for extraction relief, or both. In particular embodiments, the first included angle may be between 5 degrees and 30 degrees, between 8 degrees and 20 degrees, between 10 degrees and 15 degrees, or specifically, 12 degrees, as examples. Further, in certain embodiments, the second included angle may be between 1 degree and 20 degrees, between 2 degrees and 10 degrees, between 3 degrees and 6 degrees, or specifically, may be 4 degrees, for example.

Other embodiments may not expand internally finned tubing to form an interference fit with holes in external fins (e.g., act 184 or 184 and 185). For example, in some embodiments, internal fins may be extruded with the desired end shape (e.g., with crevices or nucleate boiling sites). In some embodiments, an interference fit may be created between such tubing and external fins in another manner, such as by shrinking the external fins to form an interference bond, by assembling tubing and external fins at different temperatures to form an interference fit, by helically winding external fins around the tubing, or the like. Other embodiments may bond tubing to external fins in other ways, such as by welding, with an adhesive, by crimping or clamping, or by brazing or soldering, as examples. Still other embodiments may form external fins during the extrusion process when the tubing and internal fins are formed, for example. Further, some embodiments may omit external fins, as yet another example.

In a number of embodiments, the invention also provides various heat exchangers for effectively transferring heat energy between a first fluid and a second fluid, for example, and various enhanced evaporators for use in an air conditioning unit for residential use, for instance. In some embodiments, these may include multiple sections of tubing (e.g., extruded aluminum tubing), each section of tubing may have at least one tube wall defining an interior passageway, and each section of tubing may further have multiple internal fins projecting into the passageway from the tube wall. In particular embodiments, each internal fin may have at least one or multiple crevices forming at least one or multiple nucleation boiling sites. Further, in various embodiments, multiple external fins may have holes, and the multiple sections of tubing may pass through the holes and form an interference fit with the holes, for example, certain such heat exchangers may also include multiple 180 degree bends or fittings joining the multiple sections of tubing. The invention also provides, in particular embodiments, certain air conditioning units and HVAC systems having such heat exchangers or evaporators, as further examples.

Various embodiments of the invention include various combinations of such structural features, functions, or acts, other structural features, functions, or acts described herein or known in the art, or a combination thereof. 

1. Enhanced tubing for conducting heat between a first fluid within the tubing and a second fluid exterior to the tubing, the tubing comprising: at least one tube wall defining an interior passageway; and multiple internal fins projecting inward from the at least one tube wall, each internal fin having an external surface comprising multiple acute interior angles.
 2. The tubing of claim 1 the internal fins having sides) wherein at least multiple of the acute interior angles are formed in the sides of the internal fins.
 3. The tubing of either claim 1 wherein at least a portion of the acute interior angles are formed between the internal fins and the tube wall.
 4. The tubing of claim 3 wherein each internal fin has a first side and a second side, and wherein for each of the internal fins, a first acute interior angle is formed between the first side of the internal fin and the tube wall, and a second acute interior angle is formed between the second side of the internal fin and the tube wall.
 5. The tubing of claim 1, each internal fin having a center, wherein each of the internal fins comprises one of the acute interior angles at the center of the internal fin.
 6. The tubing of claim 1 wherein the tubing has a centerline and the multiple internal fins are parallel to the centerline.
 7. The tubing of claim 1 wherein the tubing has a centerline and the acute interior angles are parallel to the centerline.
 8. The tubing of claim 1 wherein the tubing has a centerline and the multiple internal fins are helically wound around the centerline.
 9. The tubing of claim 1 wherein the tubing has a centerline and the acute interior angles are helically wound around the centerline.
 10. The tubing of claim 1 wherein each internal fin further comprises an elongated slit therein.
 11. The tubing of claim 10 each internal fin having a center, wherein the elongated slit is in the center of the internal fin.
 12. The tubing of claim 1 wherein the multiple internal fins include at least four internal fins.
 13. The tubing of claim 1 wherein multiple of the acute interior angles is between 20 and 85 degrees.
 14. The tubing of claim 1 wherein each of the multiple internal fins comprises at least one convex rounded surface between at least two of the acute interior angles.
 15. The tubing of claim 1 wherein each of the multiple internal fins comprises multiple convex rounded surfaces between the acute interior angles.
 16. The tubing of claim 1 further comprising a first straight section of tubing, a second straight section of tubing, and a 180 degree bend between the first section and the second section.
 17. The tubing of claim 1, the tube wall having an exterior surface, the exterior surface comprising scalloped relief areas.
 18. The tubing of claim 17 wherein there is one of the scalloped relief areas across the tube wall from each one of the internal fins.
 19. A method of making a heat exchanger that has enhanced heat transfer characteristics, the method comprising in any order at least the acts of: forming tubing having at least one tube wall defining an interior passageway, and multiple internal fins projecting inward from the at least one tube wall; stacking multiple exterior fins, each exterior fin having multiple holes therethrough, wherein the act of stacking includes lining up the holes in the multiple exterior fins; passing the tubing through the holes in the multiple exterior fins; expanding the tubing to create an interference fit between the tubing and the holes; and modifying the internal fins to create more effective nucleate boiling cavities.
 20. A heat exchanger for effectively transferring heat energy between a first fluid and a second fluid, the heat exchanger comprising: multiple sections of tubing; each section of tubing having at least one tube wall defining an interior passageway; each section of tubing further comprising multiple internal fins projecting into the passageway from the at least one tube wall, each internal fin having multiple crevices forming nucleation boiling sites; multiple external fins having holes, wherein the multiple sections of tubing pass through the holes and form an interference fit with the holes; and multiple 180 degree bends joining the multiple sections of tubing. 